The way I see it, he's a young, charismatic, handsome black candidate. His novelty won't wear off until after he's been in the White House a few months. By a show of hands: how many of us thought we would see such a candidate in our lifetimes? Now multiply that surprise by a factor of 10 for the fanatic crowd. They'll be around for a while.
No, I don't worry about his excitement level wearing down during the general election. I'm more worried about the backlash against him should he actually win the presidency and not cause the sky to rain gold. Being that I actually like the guy, part of me hopes he doesn't win. The next president will be stepping into a mess. Electing Obama would be viewed by many as a leap of faith. If he doesn't exceed expectations, I don't see him being re-elected. I'd almost rather one of these political greybeards take the heat.